I think those characters represent the option key symbol set. You know how when you press Option and a letter (w/ or w/o a shift) you get a symbol?

Now do the reverse and find out what letters are pressed in conjuction with the Option key to get those symbols. That would be my best guess anyway. (Also note that symbols can be different. For example, option-shift-K gives  while option-K gives ˚.)

I'm thinking that it has something to do with creating them on the keyboard, with the ASCII characters.. like option+P = the pi character, so the character is p. I haven't gotten far on this one, though.